Variation

• Variation exists between different species- interspecific variation
• Variation exists between members of the same species- intraspecific variation

• Sampling is used to measure variation
• It takes measurements of individuals, selected from the population of organisms which is being investigated
• If these individuals are representative of the population as a whole then the measurements can be relied upon

Sampling is unreliable when:

• There is sampling bias- biased selection process
• Chance- no sampling bias, but individuals simply aren't representative

• Random sampling- eliminates as much as possible any human involvement in choosing samples. E.g. divide study area into grid of numbered lines, use random numbers to obtain coordinates and take samples at intersections
• Use large sample size- smaller probabililty of chance affecting result
• Analysis of collected data- statistical tests determine the extent to which chance may have influenced data

• Genetic differences
• Environmental influences

• Mutations
• Meiosis
• Fusion of gametes

• pH
• Sunlight
• Temperature
• Rainfall
• Soil conditions
• Food availability